1. Field of the Invention
This invention relates generally to a system and method for identifying objects and, more particularly, to a system for identifying objects having transceiver tags.
2. Description of Related Art
Automatic identification systems employing radio sensitive tags have been proposed for tracking of people, animals, vehicles and baggage. For example, U.S. Pat. No. 5,204,681, issued Apr. 20, 1993 to Greene, describes a system having a target affixed to an object to be identified, a transmitter for generating interrogation signals, and a receiver having a signal processor for detecting a target. Each target includes multiple resonators resonant at respective frequencies. The resonant frequencies associated with a particular target are a subset of the frequencies detectable by the receiver, and provide the target with identification data.
A problem with the system described in U.S. Pat. No. 5,204,681 is that the system may not be able to identify a target in the presence of other targets. When more than one target is present, the signal processor may be unable to correlate the combination of detected resonant frequencies with any particular target, because the detected combination will not correspond to any one target, but will instead correspond to the combined set of resonant frequencies from all of the targets.
This problem may be addressed to some extent with a detection amplitude threshold for each resonant frequency. With this thresholding scheme, the signal processor does not consider a resonant frequency to be present unless the received amplitude is over the threshold. A problem with this scheme is that, in order to identify each object, the movement of the objects relative to the transmitter and receiver must be highly regimented such that at any one time only one target is transmitting signals to the receiver above the threshold.